JP2922078B2 - Silicon rod manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a silicon rod from granular silicon. More specifically, the granular silicon is partially melted in the cylindrical body, the cylindrical silicon is formed without contacting the molten silicon with the cylindrical wall due to the surface tension of the molten silicon, and the silicon is prevented from being mixed with impurities from the cylindrical wall. It is intended to provide a method for producing a crystalline or single-crystal silicon rod.

[0002]

2. Description of the Related Art A CZ method is mainly used for producing a single crystal silicon rod from granular silicon. In this method, a granular crystal silicon is filled in a quartz crucible, and the whole is melted in the crucible, and then a single crystal is formed. However, in the above-mentioned CZ method, there is a problem that impurities such as oxygen and aluminum are often eluted from the quartz crucible, and the impurities are mixed into the manufactured silicon rod.

On the other hand, a continuous casting method of a polycrystalline silicon rod from granular silicon by high-frequency induction heating is known (JP-A-61-52962, JP-A-1-264).
920, JP-A-2-30698). This method melts the entire granular silicon in the crucible by high-frequency induction heating while continuously supplying granular silicon into a bottomless crucible composed of a plurality of conductive walls divided in the circumferential direction, and continuously casts it. Things. In this method, the magnetic force generated from the current flowing through the conductive wall of the crucible and the magnetic force generated from the current flowing through the molten silicon due to the electromagnetic induction repel each other, and the molten silicon is repelled by these magnetic repulsion forces. The molten silicon is non-contact with the crucible to force it to float from the crucible.

[0004]

However, it is difficult to completely prevent the molten silicon from coming into contact with the crucible wall even in the above-described high-frequency induction heating method. There is a problem that impurities are mixed.

[0005] Therefore, in a method for producing a silicon rod by melting and solidifying granular silicon, it has been desired to develop a method for preventing contact between the molten silicon and the crucible and free from contamination from the crucible.

[0006]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems. As a result, the surface tension of molten silicon is very high, and
Paying attention to the fact that granular silicon sinters at a temperature slightly lower than the melting point and solidifies particles, succeeded in solidifying molten silicon while holding it at a position away from the crucible wall, and completed the present invention I came to the proposal here.

That is, according to the present invention, a non-conductive cylinder, which is installed so that its major axis substantially coincides with the vertical line, is filled with granular silicon, and then a part of the non-conductive cylinder in the longitudinal direction is locally localized. Heating to form a sintered part of granular silicon and a molten part of silicon, and moving the local heating area to form a solidified part by cooling the molten part while sequentially moving the sintered part and the molten part. A method of manufacturing a silicon rod.

The method of the present invention utilizes the fact that when granular silicon having a low bulk specific gravity is melted and contracted in volume, the large surface tension causes the molten silicon to become cylindrical. That is, the bulk specific gravity is small, for example, 1.0 to
When 1.5 g / ml of granular silicon is melted, the bulk specific gravity becomes 2.55 g / ml of molten silicon, and the apparent volume is reduced to about 1/2. When the granular silicon is locally heated in a state of being filled in the cylindrical body, a sintered part of the granular silicon and a molten part of the silicon are formed, and the lower part of the molten silicon is fixed by cooled and solidified silicon, and the upper part of the molten silicon is sintered. It is fixed with the tied granular silicon. Since the volume-contracted molten silicon is fixed vertically, it gathers at the center of the long axis of the cylindrical body due to surface tension to form a cylinder. as a result,
There is no contact between the wall of the cylinder and the molten silicon, and there is no risk of impurities of the cylinder being mixed into the molten silicon,
It is possible to avoid the contamination of impurities during the production of the silicon rod.

The granular silicon in the present invention may be either polycrystalline or single crystal, and any known silicon can be used without any limitation. In the present invention, it is necessary to perform local heating in order to form a sintered portion of granular silicon and a molten portion of silicon. Therefore, it is preferable that the granular silicon has a small thermal conductivity so that the heat of the molten portion is not easily transmitted to the sintered portion. It is preferably a body shape or a shape close to these.

The particle size of the granular silicon is not particularly limited, but a particle having a particle size of 0.7 to 1.5 mm is generally easily available. Granular silicon that can be particularly preferably used in the present invention is, for example, spherical silicon having a surface to which silicon fine powder is adhered or spherical granular silicon. Such granular silicon has the advantage that thermal conductivity between particles is small and that it is easy to sinter. Such granular silicon can be produced in a fluidized bed.

In the present invention, the above-mentioned granular silicon is filled in a non-conductive cylinder placed so that its major axis substantially coincides with the vertical line. The cylinder must be non-conductive.
When the cylinder is conductive, when high-frequency induction heating is employed as the heating means, a high-frequency induction current flows through the cylinder,
Since the entire cylindrical body is heated, the entire granular silicon filled therein is melted, and the present invention cannot be carried out. The material of the cylindrical body may be non-conductive as described above, but usually, ceramics such as alumina, silica, and silicon nitride are used. In particular, quartz glass is preferably used because the inside can be seen through and the contamination by impurities is small. The non-conductive cylinder may have any size and may be determined according to the size of the silicon rod to be produced.

The cross-sectional shape perpendicular to the long axis of the cylinder is not particularly limited, but is preferably a circle or a polygon close to a circle for uniform heating in the direction perpendicular to the long axis of the cylinder.

Next, local heating of a part of the non-conductive cylinder in the longitudinal direction is performed. The heating means may be any means as long as it can locally heat a part of the non-conductive cylinder in the major axis direction, such as high-frequency induction heating, infrared heating, and microwave heating. Etc. can be adopted. Silicon has a characteristic that its electrical resistance decreases with an increase in temperature, whereas in high-frequency induction heating, the smaller the electrical resistance, the greater the induced current flowing through the object. For this reason, when silicon is heated by high-frequency induction heating, the portion where the temperature is high becomes higher and melts, but the portion where the temperature is not sufficiently high is not heated much. Therefore, in the present invention, high-frequency induction heating can be preferably employed because local heating is easily performed.

In the heating, only a part of the non-conductive cylindrical body is locally heated in the long axis direction, but it is preferable to heat uniformly in a direction perpendicular to the long axis direction. Therefore, usually, a method of heating using a high-frequency induction heating coil having a shape surrounding the periphery of the non-conductive cylinder is preferably adopted.

By heating in this manner, a sintered portion of granular silicon and a fused portion of silicon are formed in the longitudinal direction of the non-conductive cylinder. At this time, if the heating is excessive, the molten portion becomes too large, and the molten silicon may flow out. Therefore, it is preferable to confirm the degree of heating in advance by an experiment so that the fusion zone does not become too large. In general, the length of the silicon melt in the major axis direction is
The diameter is preferably not more than １ ／ of the diameter of the solidified portion of silicon, and is usually in the range of 0.5 to 3 cm, preferably 1 to 2 cm. In order to make the size of such a fusion zone, for example, it is preferable that the output when high-frequency induction heating is employed is in the range of 5 to 10 KW at 2 MHz.

Then, by moving the local heating region relative to the non-conductive cylinder, the sintering part and the melting part are sequentially moved. At this time, when the method of moving the heating region from below to above the nonconductive cylinder is adopted, as shown in FIG.
Is formed, and a sintered portion 2 of granular silicon is formed thereon. Above the sintering section 2 is a filling section 1 of granular silicon. Below the melting part 3 is a silicon rod 4 in which the melting part 3 is naturally cooled and solidified. According to this method, a clean cylindrical silicon rod can be manufactured. However, when the particle size of the granular silicon is too large, the weight of the granular silicon particles themselves becomes larger than the bonding strength between the granular silicon particles in the sintered part,
Particulate silicon may fall from the sintered part, mix into the molten part below the sintered part, or damage the molten part.
Therefore, when employing this method, the particle size of the granular silicon is preferably 3 mm or less.

On the other hand, when the method of moving the heating area from the top to the bottom of the non-conductive cylinder is adopted, as shown in FIG.
A silicon rod 4 which is naturally cooled and solidified is formed above the silicon melting portion 3, a granular silicon sintered portion 2 is formed below the silicon melting portion 3, and further below the granular silicon filling portion is formed. It is one. In this method, since the molten silicon tends to flow downward, the molten silicon does not necessarily gather at the center of the long axis of the cylindrical body, and a somewhat curved cylindrical silicon rod is obtained. Therefore, the present invention can be applied to a method in which granular silicon having any particle size is used as a raw material.

Since the moving speed of the heating zone has an appropriate speed according to the diameter of the non-conductive cylinder, it is preferable to determine the moving speed in advance by performing a preliminary experiment. For example, when using a non-conductive cylinder having a diameter of 30 mm, it is preferable to adopt a speed of 2 to 8 mm / min.

In this way, the heating zone is moved relative to the non-conductive cylinder to form a solidified portion by cooling the molten portion while sequentially moving the sintered portion and the molten portion,
A syringe rod can be manufactured.

In the present invention, when high-frequency induction heating is employed as the heating means, heating efficiency is extremely poor only with high-frequency induction heating at the beginning of heating due to the characteristics of silicon and high-frequency induction heating described above. For this purpose, as shown in FIG. 3, in the initial stage of heating, a carbon plate is placed at a portion where heating is started, and this is heated by a high-frequency induction heating coil, so that the granular silicon is radiated by the radiant heat of the carbon plate. A method of heating can be suitably employed. At this time,
In order to uniformly perform heating in the direction perpendicular to the long axis of the non-conductive cylinder, it is preferable to rotate the non-conductive cylinder about its long axis.

According to the method of the present invention, both single crystal and polycrystalline silicon rods can be manufactured.
When a single-crystal silicon rod is manufactured, a method may be adopted in which a seed single crystal is placed at the bottom of a non-conductive cylinder, and the heating region is moved upward from below the cylinder. Since the single crystal produced by this method is often disturbed, if a single crystal for a semiconductor is to be obtained, it is preferable to further produce the single crystal by the FZ method or the like.

[0022]

According to the method of the present invention, the molten silicon can be solidified while the molten silicon and the crucible wall are kept out of contact. Further, in the method of the present invention, since the distance between the molten silicon and the crucible wall is larger than in the continuous casting method described above, heat loss is small, and the amount of heating of the crucible by the molten silicon is necessarily small. As a result, contamination of impurities from the crucible can be completely prevented.

In single crystal silicon obtained by the ordinary CZ method, the amount of oxygen mixed in by melting the quartz crucible is 20 pp.
m. Oxygen and impurities such as aluminum present in the granular silicon and trace impurities can be analyzed only after the production of the single crystal due to the limitation of the measurement method, but as described above, impurities are mixed during the production of the single crystal. It has been difficult to determine the amount of impurities contained in the original granular silicon. However, if single-crystal silicon is manufactured by combining the method of the present invention and the FZ method, impurities do not mix during the manufacturing. It can be guessed and it can be easily analyzed for trace impurities in the granular silicon.

[0024]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

Example 1 Average particle size produced in a fluidized bed as granular silicon
2 mm polycrystalline silicon was used. The major axis length is 150
mm, a quartz glass cylinder 5 having a cross-sectional area perpendicular to the major axis of 7 cm ² was set so that the major axis coincided with the vertical line as shown in FIG. 3, and granular silicon 1 was filled therein. .

In the initial state of heating, the high-frequency induction heating coil 6 outputs a carbon plate 7 of 7 KW (frequency is 2 KW).
MHz), and the cylinder 5 was rotated at 5 rpm until the granular silicon 1 reached a temperature sufficient for induction heating by radiant heat from the carbon plate 7.

After confirming that high-frequency induction heating was applied to the granular silicon, the carbon plate was removed, and at the same time, the high-frequency output was reduced from 7 KW to 5 KW, and granular silicon near the high-frequency induction heating coil was melted. Was made to be in a sintered state.

After the above steady state was established, the entire cylinder 5 was lowered at a moving speed of 5 mm / min, and the heating area was raised relatively. During the movement of the heating zone, the high frequency output was maintained at 5 KW so that the state of sintering, melting and solidification did not change.

Thus, a polycrystalline silicon rod having a diameter of 20 mm and a length of 120 mm was manufactured. The obtained silicon rod was pulled up to a single crystal by the FZ method, and the analysis value is shown in Table 1 as Sample A.

For comparison, the same granular silicon used above was shaken vigorously in a quartz tube to intentionally mix the quartz component, and then a single-crystal silicon rod was formed in the same manner as described above. The sample was manufactured, and its analysis value is shown in Table 1 as Sample B. Sample C is an analysis value obtained by processing a silicon rod prepared by the Siemens method into a rod shape for comparison and single crystallizing the same by the FZ method.

As shown in Table 1, the analysis values of aluminum and oxygen of Sample A are very close to those of silicon manufactured by the Siemens method, and are free from impurities. In addition, since the amount of oxygen in the general single crystal silicon manufactured by the CZ method is 20 ppm-atom, it is understood that the silicon rod manufactured by the method of the present invention has extremely high purity.

[0032]

[Table 1]

Example 2 A polycrystalline silicon rod was manufactured in the same manner as in Example 1 except that the moving direction of the cylinder was reversed. The obtained silicon rod had a somewhat curved cylindrical shape as compared with that obtained by the method of Example 1. As a result of producing a single crystal from this silicon rod in the same manner as in Example 1, and analyzing the result, the amount of impurities was exactly the same as in Example 1.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a representative method of the present invention.

FIG. 2 is a schematic diagram of another exemplary method of the present invention.

FIG. 3 is a perspective view of a representative method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Filled part of granular silicon 2 Sintered part of granular silicon 3 Melted part of silicon 4 Solidification part 5 Non-conductive cylinder 6 High frequency induction heating coil 7 Carbon plate

Claims (1)

(57) [Claims] 1. A non-conductive cylinder, which is installed so that its major axis substantially coincides with a vertical line, is filled with granular silicon, and then a portion of the non-conductive cylinder in the longitudinal direction is locally heated to obtain a granular material. Forming a sintered portion of silicon and a molten portion of silicon, and moving the local heating region to sequentially move the sintered portion and the molten portion while forming a solidified portion by cooling the molten portion. Manufacturing method of a silicon rod.